Installing hardwood stair treads is not a quick and easy DIY project.
If you are confident in your construction abilities and are a patient person, you can probably do this project yourself, else you should hire a professional to do this for you.
Flooring or Treads
Decide whether you are going to use wood flooring on the stair treads or purchase a new wood stair tread and stain it to match your wood floor.
If you are going to use wood flooring on the stair tread, you will need wood stair nosing trim to match your wood flooring or you can use unstained hardwood stair nosing that you can stain to match the rest of your floors.
Decide whether you want your stair risers (the vertical piece between each stair tread) to be stained wood, painted, or tiled.
Remove the carpeting, carpet pad, tack strips, and all the staples from your stairs.
Clean underneath the carpet since there may be dirt, drywall mud, and debris.
If you have large imperfections in your wood sub floor, sand those to make the sub floor smooth.
Make sure the stairs do not have any squeaks. Make sure the steps are level and shim any that are not to remove squeaks. Long screws tighten down the stair treads and can also eliminate squeaks.
Cut off the stair nosing (the part of the stair tread that extends past the riser) so that a new nosing can be installed.
Take measurements in 3 places on the underside of the stair tread for the depth of the nosing.
Measure the distance on the top of the nosing and draw a straight line from one side of the stair tread to the other.
Use a circular saw to cut the tread and a jigsaw to finish off the ends.
If you are painting your risers and have a decent finish on your wood, then sand and paint them.
If you are tiling your risers, make sure the risers have a smooth surface and tile them.
If you want stained risers, add new stain grade wood.
You should measure all of your risers individually since the probably are not all the same measurements.
Cut your wood for the risers and install them using finishing nails.
Nail your boards in the very bottom of the riser and very top of the riser since those areas will be covered with stair nosing or stair treads.
Measure each stair tread individually to get the measurements for your nosings and install them using finishing nails.
Measure all of your stair treads individually since they are probably not all the same size.
Cut the hardwood for the stair treads and install with adhesive to avoid nail holes or install your hardwood flooring.